In a network environment, a network controller or adapter on a host computer, such as an Ethernet controller, Fibre Channel controller, etc., will receive Input/Output (I/O) requests or responses to I/O requests initiated from the host. Often, the host computer operating system includes a device driver to communicate with the network controller hardware to manage I/O requests to transmit over a network. Data packets received at the network controller are often stored in an available allocated packet buffer in the host memory. The host computer may implement a protocol to process the packets received by the network controller that are stored in the packet buffer, and access any I/O commands or data embedded in the packet.
For instance, the computer may implement the Transmission Control Protocol (TCP) and Internet Protocol (IP) to decode and extract the payload data in the TCP/IP packets received at the network adapter. IP specifies the format of packets, also called datagrams, and the addressing scheme. TCP is a higher level protocol which establishes a virtual connection between a destination and a source. Another protocol, Remote Direct Memory Access (RDMA) establishes a higher level connection and permits, among other operations, direct placement of data at a specified memory location at the destination.
In many systems, the central processing unit of the host computer may have a cache in which data may be stored in anticipation that the cached data may satisfy an upcoming processor operation. The central processing unit can frequently read data more quickly from the central processing unit cache as compared to the host memory. As a consequence, if the proper data has been cached in the central processing unit cache, processing of that data can often be facilitated.
There are a number of data caching techniques for selecting the data to be cached. Many of these techniques are based on a “hit” or “miss” strategy. If target data requested by the central processing unit is found in the central processing unit cache, a “hit” occurs which provides positive feedback to continue selecting data for caching using the current criteria. Conversely, if target data requested by the central processing unit is not found in the central processing unit cache, a “miss” occurs which provides negative feedback. Once a certain number of misses occurs, the criteria used to select data for caching may be changed in an attempt to increase the frequency of cache hits.
If processing of data is initiated with an empty cache, a significant number of cache misses may be incurred as the cache is filled. One technique for increasing cache efficiency is to “warm” the cache by placing data in the cache prior to initiating processing of the data. A cache may be warmed by placing prefetch instructions in the network controller driver. For example, a driver for the network controller may provide prefetch instructions to the central processing unit to place headers of selected packets in the central processing unit cache in anticipation of that header information being needed by the processor. However, in many systems, the central processing unit is not obligated to act on such prefetch instructions from the driver. As a consequence, significant data access latency may occur as the cache is filled as processing of the data packets is initiated.